Re: is Vax addressing sane today

MitchAlsup1 <mitchalsup@aol.com> wrote:

On Sun, 8 Sep 2024 21:09:39 +0000, Lawrence D'Oliveiro wrote:
 

On Sun, 8 Sep 2024 17:56:55 +0000, MitchAlsup1 wrote:
 

The problem with VAX was NOT that one could not put a lot of work in a
single instruction;
 
no,
 
The problem with VAX is that it made putting too much work in a single
instruction easy.

 
Perhaps there is also the issue of the wildly-variable instruction
length.
A single VAX operand descriptor could be up to 6 bytes; I think the
instruction with the most general-format operands could have 6 of them:
so, plus opcode, such an instruction could be 37 bytes long.

 
I have not heard an argument that the complex things in VAX ISA are
a) desirable
b) performance helpful

Speaking of complex things, have you looked at Swift output, as it checks
all operations for overflow?

You could add an exception type for that, saving huge numbers of correctly
predicted branch instructions.

The future of programming languages is type safe with checks, you need to
get on that bandwagon early.

I (sort of) think VAX ISA as a grown up PDP-11, ignoring all the
dastardly complicated instructions it inflicted upon itself. AND
it did inflict those things upon itself.
 
Restricting a new-VAX-like ISA to 1-2-3 Operand and 1-result with
at most 1 exception would result in a MUCH cleaner and easier to
build machine.
 

While the shortest instruction could be just 1 byte.
 
Even those who are talking about “post-RISC” are, I think, still in
favour of RISC-style fixed instruction lengths.

 
I, for the record, are in favor of fixed length instruction-specifier
followed by constants the entirety is the instruction, while the
former minimizes your ability of shooting yourself in the foot.